A recent television broadcasting system, for example, can broadcast a number of program contents to a viewer, as multi-channel broadcasting is developed along with a widespread use of digital broadcast. Also, the number of services that distribute video contents has been increasing along with a widespread use of the high-speed internet in the internet environment.
Adjunct data (for example, data broadcast in the digital broadcast) of data signals are sometimes added to a stream of contents distributed by such a digital broadcasting system or a contents distribution service of the internet or the like. The adjunct data may include link information such as an URL (Uniform Resource Locator: Internet Address).
In the contents distribution service, it is necessary to protect a copyright of contents to be distributed by preventing an unauthorized use of the contents by a malicious user. As one of known arts, for example, there is a metadata utilization control system capable of protecting a right of a broadcast station by utilizing contents only with metadata signed by a metadata provider granted by the broadcast station (see Patent Document 1, for example).
With regard to the contents distribution service, it is also necessary to ensure a security of the contents to a viewer. This is because not only a stream of legitimate contents, a contents reception apparatus may also receive, for example, a stream which is after a while switched to an unintended fraudulent stream containing a packet whose relationship with its previous or following packet is not guaranteed.
As for the digital broadcast, the reception apparatus may receive a fraudulent stream to which so-called “spoofing” is performed, with a falsified data broadcast in which interactive communication is possible, and image data and audio data both of which are remain intact. In such a case, there is a concern that a user accesses to the URL included in the data broadcast with believing that information should be safe as it is distributed by a trustworthy broadcast station, which may result in damaging the user seriously by phishing and the likes.
Hence, in the contents distribution service, it is necessary to ensure the security of the contents and, as one method for that purpose, a stream authentication is a known scheme to ensure legitimacy of the stream by adding a signature to authenticate sender identification to the contents.
As stated above, if a transmission apparatus transmits a stream with contents whose security is ensured by the stream authentication, the reception apparatus may refrain from playing the stream received until it is ensured to be legitimate (that is, during a process of authentication), which may prevent inflicting a disadvantage on the user.    Patent Document 1: Japanese Patent Application Laid-Open No. 2006-254234